The present invention relates to methods of forming monomolecular chemisorption films obtained by chemisorbing adsorbate molecules on a surface of a base material. More particularly, the invention relates to methods of forming monomolecular chemisorption films used for antifouling films, liquid crystal alignment layers, polarizing films, retardation films, conductive films for molecular devices or the like. The invention further relates to methods of manufacturing liquid crystal display devices utilizing such thin films.
Monomolecular thin films (also referred to as xe2x80x9cmonomolecular chemisorption filmsxe2x80x9d) have conventionally been produced by the methods comprising the steps of immersing a base material in a chemisorption solution containing a nonaqueous organic solvent and an adsorbate at a relatively low concentration for a predetermined time, thereafter react the adsorbate with the surface of the base material, and thereafter washing the unadsorbed molecules away from the surface of the base material. In such conventional methods, since the chemisorption solution contains the adsorbate at a low concentration, the adsorbate is not excessively adsorbed to the surface of the base material. Therefore, uniform monomolecular films can be readily obtained. In addition, since the adsorbate is lost little in the step of washing, the adsorbate can be efficiently used, leading to high cost efficiency in production.
However, in such conventional methods, it takes a long time to react the adsorbate with the base material, and therefore the base material needs to be immersed in the solution for a long time, leading to poor production efficiency. For example, in the case where the chemisorption solution contains a silane-based surface active agent (an adsorbate) having a linear hydrocarbon chain group and Si at a concentration of 1% by weight, the base material needs to be immersed in the solution for approximately two hours.
In view of such a drawback in the conventional methods, various attempts to improve the production efficiency have been made, but heretofore no such attempts have been successful in achieving a simple and effective method. For example, by heating the chemisorption solution, it is possible to improve the reactivity and thereby to reduce the time for immersing the base material to a certain extent. However, when the chemisorption solution is heated, such disadvantageous effects are incurred that the solvent is evaporated or boiled in the immersing reaction and that the decomposition or side reaction of the adsorbate molecules is caused, and thus it is difficult to produce good uniform monomolecular chemisorption films. In addition, by heating the solution, the amount of evaporating solvent increases, and this requires a consideration for providing special explosion-proof facilities. Due to such drawbacks, it is generally undesirable to heat the chemisorption solution to a temperature higher than 80xc2x0 C., but heating the solution up to such a temperature only reduces the reaction time by about 10-20%.
It is, on the other hand, also possible to reduce the time for immersing the base material by increasing the concentration of the adsorbate in the solution. However, the increase of the concentration of the adsorbate induces such a drawback that the adsorbate is excessively attached onto the substrate surface, which results in a difficulty in forming uniform monomolecular films and a poor utilization efficiency of the adsorbate.
In view of the foregoing and other drawbacks in prior art, it is a primary object of the present invention to provide methods of forming monomolecular chemisorption films that are excellent in uniformity and molecular alignment property and usable for liquid crystal alignment layers. More specifically, it is a first object of the present invention to provide methods of forming extremely thin monomolecular films which is formed to have a thickness at the nanometer level within a short production time.
It is a second object of the invention to provide methods of forming such monomolecular films capable of controlling an alignment of liquid crystal molecules in a predetermined direction (for example, liquid crystal alignment layers).
It is a third object of the invention to provide methods of manufacturing liquid crystal display devices utilizing such liquid crystal alignment layers.
In order to accomplish the foregoing and other objects, the present invention provides the following methods:
(1) The present invention provides methods of forming a monomolecular chemisorption film comprising at least the steps of: forming a solution layer on a surface of a base material by contacting the chemisorption solution with the surface of the base material in a dry atmosphere, the chemisorption solution including a silane-based surface active agent and a nonaqueous organic solvent; and chemisorbing molecules of the surface active agent onto the surface of the base material by evaporating the organic solvent contained in the solution layer in the dry atmosphere.
In the above-described method, the chemisorption solution is applied onto the base material sufficiently but not excessively to form the solution layer formed of the chemisorption solution, and thereafter the chemisorption solution is concentrated on the surface of the base material. By employing this method, the chemisorption reaction proceeds in a remarkably efficient manner. Accordingly, a monomolecular thin film can be formed within a short time.
Now, the technical significance of the above-described constitution of the invention is explained below. Ideally, in a monomolecular chemisorption film formed on the surface of the base material, the adsorbate molecules are bonded to the surface of the base material at one end of the molecules, and are arrayed along the surface of the base material in a monolayer-like manner. In order to form such an ideal chemisorption film, the chemical adsorbate molecules need to be bonded sufficiently but not exceedingly to all the possible positions on the surface where the molecules can be adsorbed. For this purpose, it is preferable that the concentration of the chemisorption solution should be made low so that the adsorbate molecules can move freely. However, when the concentration of the solution is low, it takes a long time to adsorb the molecules to all the possible positions, and therefore the production efficiency is poor. Nevertheless, by employing the above-described method, since the solution is concentrated after applied onto the base material, the adsorbing reaction can be completed within a short time even in the case of the solution having a low concentration. In addition, since the solution has a low initial concentration, the affinity of the solution with the base material is good, and a thin, uniform coating layer (solution layer) can be formed on the base material. As a result, excessive use of the chemisorption solution is eliminated and uniform thin films are readily formed. Moreover, the concentration of the adsorbate molecules on the base material gradually increases corresponding to the evaporation of the solvent, resulting in a smooth chemisorption reaction. Consequently, in comparison with the case of the solution having a high initial concentration, it is possible to form a chemisorption film with a higher quality in which unadsorbed molecules remaining on the base material is less, and a density of the adsorbed molecules is higher. According to the experiments by the present inventors, by employing the above-described method, the reaction time was reduced to approximately 1 to 11 minutes, whereas in conventional methods (immersing reaction methods) the time was approximately 1 to 2 hours.
(2) The above-described method (1) may be such a method comprising the steps of: accelerating a chemisorption reaction by evaporating the organic solvent and concentrating a silane-based surface active agent contained in the solution layer; aging to complete the chemisorption reaction for a predetermined time, after the evaporating organic solvent; and washing the surface of the base material with a nonaqueous organic solvent to remove unadsorbed surface active agent remaining on the surface of the base material.
The reaction (chemisorption reaction) in the above-described method is gradually accelerated until the concentration of the surface active agent in the solution layer reaches 100%, and the aging is allowed to further continue thereafter. According to this method, the accelerating of the chemisorption reaction by the concentrating and the aging complement each other, and the chemisorption reaction can proceed smoothly and quickly. In the above-described step of aging, the concentration of the surface active agent molecules has already reached 100% and the reactivity of the solution has become high, and therefore, the chemisorption reaction can proceed further even in the case where the adsorbing reaction has not been completed when the evaporation of the solvent is finished. Accordingly, the chemisorption reaction is performed in a remarkably efficient manner.
In addition, by employing the above-described method, when the adsorbate molecules has a low reactivity, or when the solvent evaporates at a high evaporation rate, it is only necessary to increase the time for the aging, and therefore, regardless of the properties of the adsorbates or the solvents, the reduction of the reaction time can be achieved without spoiling the quality of the thin films.
In addition, the above-described method comprises the step of washing the unadsorbed molecules remaining on the surface of the base material to remove the molecules from the surface after the step of the aging, and this step serves to form a uniform monomolecular thin film. The technical significance of the step of washing is as follows. In order to form a uniform monomolecular chemisorption film, the adsorbate molecules need to be chemically bonded to all the possible positions (generally, hydrophilic groups) on the surface of the base material sufficiently but not excessively. However, it is difficult to equalize the number of the adsorbate molecules in the solution layer to the number of the possible positions (active sites) on the surface of the base material where the molecules can be adsorbed. For this reason, it is necessary that the number of the adsorbate molecules such as surface active agent molecules to be applied on the surface of the base material should be more than the number of the possible positions where the molecules can be chemically adsorbed. Thus, at the completion of the chemisorption reaction, unadsorbed molecules remain on the surface of the base material. The unadsorbed molecules inhibit the formation of monomolecular chemisorption films by, for example, attaching onto the chemisorption films. However, by washing the surface of the base material after the aging, the molecules other than those adsorbed on the substrate, i.e., the unadsorbed molecules can be removed, and thereby a high-quality monomolecular chemisorption film in which adsorbed molecules are arrayed along the surface of the substrate in a monolayer-like manner can be formed.
(3) In the methods as described in (1) and (2), the dry atmosphere may be an atmosphere having a relative humidity of 30% or less.
In the method of the present invention, the silane-based surface active agent that can be adsorbed on the surface of the base material is used for forming methods of the present invention, and such a silane-based surface active agent has a property such that it reacts with water. Therefore, if the above-described methods are performed in an atmosphere having a high humidity, the silane-based surface active agent reacts with the moisture in the atmosphere, spoiling the reactivity with the base material and causing turbidity in the chemisorption film. By employing the atmosphere having a relative humidity of 30% or less, the adsorbing reaction can proceed without causing such a problem.
Examples for the atmosphere having a relative humidity of 30% or less may include an air atmosphere having a relative humidity of 30% or less. In addition, an inert gas having a relative humidity of 30% or less may be employed. Further, means for heating, decompression, blasting may be employed for preparing these atmospheres.
(4) In the methods as described in (1) to (3), it is preferable that the chemisorption solution is a nonaqueous organic solvent having a boiling point of 100 to 250xc2x0 C.
Since the organic solvent having a boiling point of 100 to 250xc2x0 C. has an appropriate evaporation rate at the room temperature (25xc2x0 C.), such solvent is desirable in performing the accelerating the chemisorption by the concentration of the solution at the room temperature (25xc2x0 C.). In other words, by employing the organic solvent with the above-described boiling point, the reduction of the reaction time is achieved and at the same time, high-quality chemisorption films can be formed.
(5) Each of the nonaqueous organic solvent in the chemisorption solution and the nonaqueous organic solvent employed in the step of washing in the methods as described in (1) to (3) may have a functional group selected from the group consisting of an alkyl group, a fluorocarbon group, a chlorocarbon group and a siloxane group.
The above-described organic solvent having the functional groups is highly capable of dissolving the silane-based surface active agents, and moreover, the solvent absorbs little water and can be easily dehydrated. Accordingly, such an organic solvent is desirable as a solvent of the adsorbate, and can be suitably used for a solvent for washing the unadsorbed molecules.
(6) It is preferable that the organic solvent having a siloxane group in the method as described in (5) be a silicone-based solvent. The silicone-based solvent absorbs little water, and the water contained in the solvent can be readily dehydrated. In addition, the silicone-based solvent is excellently cosoluble with the silane-based surface active agent. Accordingly, an adsorbing reaction can proceed smoothly and the high-quality chemisorption film can be formed.
(7) The surface active agent as in the methods as described in (1) to (6) may be a mixture of a plurality of surface active agents having a different critical surface energy each other.
When such a mixture of a plurality of surface active agents is employed, the resulting chemisorption film becomes such that the molecules of each type of surface active agents are adsorbed on the base material in a mixed state, and the property of the resulting film becomes such that both types of the adsorbed molecules are mixed. Therefore, the properties of the chemisorption film, such as a water repelling property and oil repelling property, can be finely controlled by adjusting the combinations of the critical surface energies of the surface active agents and by varying the mixing ratios of the surface active agents, and in the case of utilizing the chemisorption film as a liquid crystal alignment layer, the alignment control performance for liquid crystal molecules can be arbitrarily adjusted. In addition, the chemisorption methods according to the present invention exhibits the above-described advantageous effects by comprising the steps of an accelerating reaction and an aging in the case of using such multi-component chemisorption solution as well.
(8) The surface active agent in the methods as described in (1) to (6) may be a silane-based surface active agent comprising one of a linear carbon chain and a linear siloxane chain; and at least one silyl group selected from the group consisting of a chlorosilyl group, an alkoxysilyl group and an isocyanatosilyl group.
These silane-based surface active agents are excellent in the reactivity with the base material. The chemisorption methods in the present invention performs the above-described advantageous effects in the case of using these silane-based surface active agents as well.
(9) The carbon chain or siloxane chain in the method as described in (8) may be such that an end or a part thereof is substituted by at least one organic group selected from the group consisting of a carbon trifluoride group (xe2x80x94CF3), a methyl group (xe2x80x94CH3), a vinyl group (xe2x80x94CHxe2x95x90CH2), an allyl group (xe2x80x94CHxe2x95x90CHxe2x80x94), an acetylene group (xe2x80x94Cxe2x89xa1Cxe2x80x94), a phenyl group (xe2x80x94C6H5), an aryl group (xe2x80x94C6H4xe2x80x94), a halogen atom, an alkoxy group (xe2x80x94OR, where R is an alkyl group), a cyano group (xe2x80x94CN), an amino group (xe2x80x94NH2), a hydroxyl group (xe2x80x94OH), a carbonyl group (xe2x95x90CO), an carboxy group (xe2x80x94COOxe2x80x94) and a carboxyl group (xe2x80x94COOH).
The silane-based surface active agent having the above-described organic groups is excellent in controlling the alignment of the adsorbate molecules, and is particularly suitable for forming a liquid crystal alignment layer.
(10) The methods of forming a liquid crystal alignment layer according to the present invention are now described hereinafter. The invention also provides: a method of forming a liquid crystal alignment layer comprising a chemisorption film wherein molecules of a surface active agent are chemisorbed on a surface of a substrate on which an electrode is provided, comprising at least the steps of forming a solution layer on the surface of the substrate by contacting a chemisorption solution with the surface of the substrate, the chemisorption solution including the silane-based surface active agent and a nonaqueous organic solvent; chemisorbing molecules of the surface active agent onto the surface of the substrate by evaporating the organic solvent contained in the solution layer in the dry atmosphere; and washing the surface of the substrate with a nonaqueous organic solvent to remove unreacted molecules of the surface active agent remaining on the surface of the substrate.
(11) In the method of forming a liquid crystal alignment layer as described in (10), the step of chemisorbing may comprise the steps of accelerating a chemisorption reaction by evaporating the organic solvent and concentrating a silane-based surface active agent contained in the solution layer; and aging to complete the chemisorption reaction for a predetermined time after the evaporating organic solvent.
(12) In the methods as described in (10) and (11), the step of pre-aligning the adsorbed molecules chemisorbed on the substrate surface in a predetermined direction, by pulling the substrate out in a predetermined direction in a dry atmosphere to drain-dry the solvent on the substrate surface may be provided after the step of washing.
(13) In the method as described in (12), the step of realigning the adsorbed molecules pre-aligned in a predetermined direction by irradiating the substrate surface with a polarized light is provided after the step of pre-aligning.
The steps of forming a solution layer, chemisorbing and washing in the above-described (10) and (11) are basically the same as methods of forming a monomolecular chemisorption film described in the above-described (1) to (9), except that the substrate having an electrode formed thereon is employed as the base material. Accordingly, the steps particularly required in forming a liquid crystal alignment layer are described below.
In the method as described in (12), the step of pre-aligning adsorbate molecules by pulling out the substrate in a predetermined direction to drain-dry the solvent on the substrate surface is provided after the step of washing. According to such a method, since the drain-drying of the washing solution attached on the substrate also serves for the pre-aligning treatment of the adsorbate molecules, the pre-aligned film can be formed efficiently. Next, the technical significance of drain-drying is described below. When the substrate wet with the washing solution is dried in a standing condition in the dry atmosphere, the top end of the wet surface gradually proceeds downward (in the direction of gravitation), and the drying proceeds from the top end of the wet surface towards a downward direction. The present inventors have found in the study of the above chemisorption film that the adsorbed molecules on the substrate are aligned in the direction of the drain-drying. The above-described methods are accomplished based on these findings. The alignment by a drain-drying method is referred to as a pre-alignment in the specification. The pre-aligned film can be usable for a liquid crystal alignment layer because the pre-aligned film can also control the liquid crystal molecules in a predetermined direction. However, the pre-aligned film is insufficient in the stability against external stresses such as heat and friction, when compared with the realigned layer described below (the chemisorption film after irradiating with a polarized light).
In view of the above problems, in the method as described in (13), the step of realigning by irradiating the pre-aligned film (the chemisorption film after pre-aligning) with a polarized light is added. The step of realigning after the pre-aligning makes the alignment state of the chemisorption film more stable, and increases the resistance to the external stresses such as heat and friction, and furthermore, improves the surface anchoring force over the liquid crystal molecules. The reason for providing the step of realigning after the pre-aligning is that by irradiating with such a polarized light as ultraviolet rays after pre-aligning, the adsorbed molecules can be realigned uniformly and efficiently in a predetermined direction. In particular, in the case of employing the surface active agent having a photoreactive group, by irradiating with a polarized light, the adsorbed molecules can be crosslinked or polymerized each other, and thus an even greater surface anchoring force over the liquid crystal can be obtained on the chemisorption film.
It is noted that the direction of polarization of the polarized light in the realigning is preferably crossed the drain-drying direction not at a right angle but at least an angle with a little shift from 90xc2x0, preferably more than several degrees shifted from 90xc2x0. The reason is that, when crossed at an angle of 90xc2x0, there is a possibility that the adsorbed molecules are aligned in two directions in the same probability. In addition, when the pre-aligned film is irradiated with a polarized light having the direction of polarization parallel to the drain-drying direction, the direction of inclination of the adsorbed molecules becomes identical to the direction of crosslinking, and thereby the directions of the adsorbed molecules become more uniform and the resulting realigned film has a more excellent surface anchoring force to the liquid crystal molecules.
(14) The surface active agent in the above-described methods of forming the liquid crystal alignment layer may be a mixture of a plurality of surface active agents having a different critical surface energy each other.
(15) The surface active agent in the above-described methods may be a silane-based surface active agent comprising one of a linear carbon chain and a linear siloxane chain; and at least one silyl group selected from the group consisting of a chlorosilyl group, an alkoxysilyl group and an isocyanatosilyl group.
(16) The carbon chain or siloxane chain in the above-described methods may be such that an end or a part thereof is substituted by at least one organic group selected from the group consisting of a carbon trifluoride group (xe2x80x94CF3), a methyl group (xe2x80x94CH3), a vinyl group (xe2x80x94CHxe2x95x90CH2), an allyl group (xe2x80x94CHxe2x95x90CHxe2x80x94), an acetylene group (xe2x80x94Cxe2x89xa1Cxe2x80x94), a phenyl group (xe2x80x94C6H5), an aryl group (xe2x80x94C6H4xe2x80x94), a halogen atom, an alkoxy group (xe2x80x94OR, where R is an alkyl group), a cyano group (xe2x80x94CN), an amino group (xe2x80x94NH2), a hydroxyl group (xe2x80x94OH), a carbonyl group (xe2x95x90CO), an carboxy group (xe2x80x94COOxe2x80x94) and a carboxyl group (xe2x80x94COOH).
(17) In the above-described methods, the dry atmosphere may be an atmosphere having a relative humidity of 30% or less.
(18.1) In the above-described methods, the chemisorption solution may comprise a nonaqueous organic solvent having a boiling point of 100 to 250xc2x0 C.
(18.2) In the above-described methods, each of the nonaqueous organic solvent in the chemisorption solution and the nonaqueous organic solvent used in the step of washing may have a functional group selected from the group consisting of an alkyl group, a fluorocarbon group, a chlorocarbon group and a siloxane group.
(18.3) In the above-described methods, the organic solvent having a siloxane group may be a silicone-based solvent.
(19) In the above-described methods, the chemisorption solution in the step of forming a solution layer may be applied onto the substrate surface by one of an offset printing, a screen printing, and a roll coating. The chemisorption solution may have a solution viscosity of 1 to 50000 cSt. A silicone may be used as a solvent for adjusting the solution viscosity of the chemisorption solution.
(20) The method of forming a liquid crystal alignment layer as described in (10) may further comprise the step of forming an underlayer prior to the step of forming the solution layer, wherein: another solution layer is formed on the substrate surface directly by contacting another solution to the substrate surface, the foregoing another solution wherein a chemical adsorbate having a plurality of chlorosilyl groups is dissolved in a solvent; thereafter the solvent in the foregoing another solution layer is evaporated in a dry atmosphere to form siloxane-bonds from the chemical adsorbate in the foregoing another solution layer on the substrate surface; thereafter the substrate surface is washed to remove unadsorbed molecules from the substrate surface; and the substrate surface is exposed to a moist air, so that OH groups are added to chlorosilyl groups in the molecules of the adsorbate.
The above-described step of forming the underlayer is similar to the foregoing method of forming a chemisorption film according to the present invention in which the accelerating the chemisorption reaction by the concentrating and the aging are provided, and therefore, it is made possible to form the underlayer within a remarkably short time. As the adsorbate used in the step of forming an underlayer, a chemical adsorbate having a plurality of chlorosilyl groups can be used. The chemical adsorbate having a plurality of chlorosilyl groups can be readily chemisorbed onto the substrate, and when the adsorbed molecules are exposed to an atmosphere containing moisture, unreacted chlorosilyl groups contained in the chemisorption solution are turned into the molecules having a plurality of OH groups at the surface of the substrate by causing the dehydrochlorination reaction with water. Since these OH groups have a performance as active sites where the molecules of the silane-based surface active agent can be bonded, the molecules of the surface active agent can be bonded to the surface of the substrate via the underlayer at a high density. It is noted that the more the OH groups (active hydrogen atoms) are present on the substrate surface, the higher the density of the adsorbed molecules is, and as a result, a liquid crystal alignment layer having an excellent surface anchoring force to the liquid crystal molecules and excellent durability can be obtained.
(21) A method of manufacturing a liquid crystal display device according to the present invention may have the following construction. Since the method of manufacturing a liquid crystal display device incorporates the above-described methods of forming the liquid crystal alignment layer, the details that has already been described in the above-described methods of forming the liquid crystal alignment layer are not repeated here for the sake of brevity.
The present invention provides the method of manufacturing a liquid crystal display device comprising at least the steps of forming a solution layer on a surface of a first substrate having a plurality of electrodes formed in a matrix by contacting the chemisorption solution with the surface of the substrate in a dry atmosphere, the chemisorption solution containing a silane-based surface active agent and a nonaqueous organic solvent; evaporating the organic solvent in the solution layer in a dry atmosphere and chemisorbing molecules of the surface active agent onto the surface of the substrate; washing the substrate surface having chemisorbed molecules of the surface active agent with a washing solution comprising a nonaqueous organic solvent to remove unadsorbed molecules of the surface active agent off from the substrate surface; after the step of washing, pre-aligning the chemisorbed molecules on the substrate surface in a predetermined direction by pulling the substrate out in a predetermined direction in a dry atmosphere to drain-dry the solvent on the substrate surface and to pre-align the molecules chemisorbed on the substrate; realigning the chemisorbed molecules in a predetermined direction by irradiating the pre-aligned chemisorbed molecules with a polarized light; and assembling a liquid crystal cell by opposing the first substrate having an alignment layer formed by the step of realigning and a second substrate having a counter electrode with a predetermined gap so that each of the substrate surfaces provided with the electrode faces inwardly.
(22) In the above-described method, the step of realigning in the method of manufacturing a liquid crystal display device is such that using a polarizer and a patterned mask overlaid on the polarizer, the polarized light is irradiated a plurality of times onto each pixel having a plurality of micro-sections, in such a manner that in each time the polarized lights portioned in different directions are correspondingly applied to one of the plurality of micro-sections to form an alignment layer in which each of the plurality of micro-sections has a different realigning direction.
By employing this method, the direction of realigning can be controlled at each of the micro-sections, and a multi-domain type liquid crystal display device can be realized.
It is noted that after the steps of forming a solution layer, chemisorbing, washing, and pre-aligning, the methods as described in the foregoing methods of forming a liquid crystal alignment layer can be employed.